Where the oceans
are changing.

Tide gauges measure relative sea level — the water against the land it actually meets. NOAA runs about 200 US stations; the global PSMSL network holds records more than 150 years long. It is the measurement that matters for a street, a wharf, a parcel.

Since 1992, satellite radar altimetry — TOPEX/Poseidon through the Jason series to Sentinel-6 — has measured absolute global sea surface height to millimeter precision, and SWOT now adds high-resolution 2D mapping. It is the measurement that matters for the planet.

The panel here asks the first question live: pick a NOAA station and your browser queries the CO-OPS API directly for its latest reading and its last decade of monthly means. Note how differently the same ocean behaves against different land — Grand Isle is sinking into its delta while Juneau's shoreline is rebounding upward faster than the sea can follow.

Between a six-minute reading and a century curve there is a timescale this page did not cover: the next few weeks. On 2026-09-01 Dillon Amaya, NC State posted a filtered sea surface height diagram — distance along the coast on one axis, time on the other — showing a major coastally trapped wave, set off by the developing 2026 Super El Niño, running up Mexico's Pacific coast at about 6 mph and likely in US waters within a couple of weeks.

The mechanism: El Niño slackens the trade winds, and warm water that had been piled up in the western Pacific sloshes east along the equator as a Kelvin wave. When it reaches South America it cannot go further east, so it turns and runs poleward along the continental slope, trapped against the coast. Each pulse lifts coastal sea level by 15–30 cm as it passes, and the water it leaves behind stays warm and high. Over a season a strong El Niño raises the whole California coast by a similar amount: San Francisco's monthly mean ran about 30 cm above trend in February 1998.

Why this winter is different: the tropical Pacific is already past the "very strong" line, NOAA gives a greater than 90% chance of a very strong event and a 69% chance of one stronger than anything since 1950, and the 18.6-year lunar nodal cycle peaks in 2026, so the king tides around Christmas are as high as they get. Scripps' Mark Merrifield expects "likely the highest sea levels ever recorded on the California coast." NOAA's 2026–27 high tide flooding outlook puts the Pacific coast and the Mid-Atlantic in line for the most extra flood days, on a national median of 7–12 days — a record.

A trapped wave is not visible in a single reading; it is visible in the residual — what the gauge measures minus what the tide table predicted — and in how that residual moves from one station to the next. This panel computes it live for eight open-coast NOAA stations from San Diego to Sitka. If the wave in the post arrives on schedule, it should show as a band of red walking up the rows at roughly the dashed slope.

None of these is the long-term trend, and none of them is "sea level rise" in the sense of the next section. They are what a California shoreline will actually experience this winter on top of it, and they can coincide. NOAA's William Sweet calls it a double whammy: decades of rise as the first punch, El Niño as the second. Patrick Barnard at UC Santa Cruz puts the difference at roughly 170,000 more people and $60 billion more property exposed than in a winter without one.

Not on this coast: Miami. A Pacific trapped wave stays in the Pacific; nothing in the post reaches the Atlantic. Florida's El Niño winter is a stormier, wetter one, with a higher chance of high tide flood days but no 30 cm wave. The companion Miami guide ↗ says which of these terms apply there and which do not.

The altimetry record shows about 3.4 mm/yr on average since 1993, accelerating to roughly 4.5 mm/yr in recent years — around 10 cm of total rise in three decades.

We also know why. GRACE-FO gravimetry weighs the ice sheets from orbit, and ~4,000 Argo floats profile ocean heat for thermal expansion. Add the terms up and they match what the altimeters see — the budget closes: roughly one-third thermal expansion, two-thirds meltwater.

Process-based models run under emissions scenarios. IPCC AR6 puts global mean sea level in 2100 at roughly 0.28–1.01 m above 1995–2014 depending on pathway — with low-confidence high-end tails beyond that if marine ice sheet instabilities engage.

Nearer term the pathways barely diverge: the NOAA 2022 interagency report projects ~25–30 cm along US coasts by 2050 largely regardless of scenario. And for a specific parcel, local projections add vertical land motion from GPS and InSAR — subsidence or uplift is often the dominant term, as the tide gauge panel above shows.

To see what these curves mean on the ground, I took them to one coastline: Downtown Miami Flood Risk ↗ — LiDAR terrain, the Biscayne aquifer, 2,594 injection wells, and a 3D visualiser with these same scenarios as the slider. The case study has the findings.